INTERACTION OF CALCIUM WITH SUGAR TYPE
LIGANDS IN SOLUTIONS RELATED TO THE BAYER
PROCESS
PhD. Theses
CONFIDENTIAL TO SPONSORS
ATTILA PALLAGI
Supervisors:
DR. PÁL SIPOS
DR. ISTVÁN PÁLINKÓ
DR. STEVEN ROSENBERG
Doctoral School of Chemistry
Material and Solution Structure Research Group | Department of Inorganic and
Analytical Chemistry and Department of Organic Chemistry | Faculty of Science
and Informatics | University of Szeged
Szeged
2011
1. Introduction
The gluconate (hereafter Gluc−) is known to form complexes in solution with various
metal ions. Complex solution species of Gluc– with Ca2+ and Al3+ (the two metal ions of
importance in the current work) are reasonably well established. It is well known that Ca2+
forms weak Gluc– complexes of 1:1 composition in the usual (2 < pH < 12) range. Complexes
with Al3+ and Gluc– in the same pH range are also well established.
Relatively little is known about the complexes forming in strongly alkaline solutions
(those relevant to the Bayer process) in Ca2+/Gluc–, Al3+/Gluc– binary and Ca2+/Al3+/Gluc–
ternary systems.
We found that Ca2+ ion forms stable complexes with Gluc− in pure, aqueous NaOH
solutions. The formation of Ca2+ − Gluc− complexes significantly enhances the solubility of
calcium at high pH (relative to analogous pure NaOH solutions), and the stability constants
are high enough to prevent the precipitation of Ca(OH)2 in systems with pH > 13 and
[Gluc−]T > [Ca2+]T. These high-pH complexes are formed via binding the calcium ion to the
(deprotonated) alcoholate moiety on the C2 and/or C3 positions of gluconate, forming
bonding isomers. At pH ≥ 12 the predominant solution species formed are polynuclear in
nature.
The Al(OH)4− was also found to form stable complex with gluconate in alkaline solutions.
The formation of this complex does not involve binding or release of hydroxide ions; most
probably condensation takes place with the release of water.
Potentiometric titration curves obtained for the Ca2+/Al(OH)4−/Gluc− ternary systems are
markedly different from the sum of those found for the binary systems indicating the
formation of complexes comprising of these three components (i.e., ternary complexes). In
these systems intense proton exchange is observed, which is a sign that the ternary complex is
of extremely high stability.
2
2. Experimental
All materials [calcium chloride (CaCl2, Molar Chemicals, puriss), hydrogen chloride
(HCl), sodium hydroxide (NaOH, VWR, a.r grade), sodium gluconate (NaGluc, SigmaAldrich, ≥ 99 %), sodium heptagluconate (NaHglu, Sigma-Aldrich), glucose (Gls, SigmaAldrich, ACS reagent), calcium heptagluconate (CaHglu2, Sigma-Aldrich, ≥ 98.0 %), sorbitol
(Sigma-Aldrich, ≥ 98 %), arabic acid (HAra, Sigma-Aldrich), mucic acid (H2Muc, SigmaAldrich, ≥ 97 %), aluminium wire (J. M. & Co, 99.99 %) ] used for experiments were used as
received without any further purification. The preparation of the carbonate-free sodium
hydroxide solutions and of the Al(OH)4− solutions were performed according to wellestablished procedures.
The NMR analysis of the samples were carried out using a BRUKER Avance DRX 500
NMR spectrometer equipped with a 5 mm inverse broadband probe-head furnished with z
oriented magnetic field gradient capability. Experimental protocol was also built to record
43
Ca or 27Al NMR spectra, respectively.
Potentiometric titrations were performed with the Metrohm 888 Titrando package using
home-made platinised-platinum hydrogen (H2/Pt) indicator electrode and Ag/AgCl reference
electrode.
Molecular modelling was performed using Hartree−Fock ab initio calculations applying
the 6-31G** basis set included in the Hyperchem program package. The Ca K-edge X-ray
absorption spectra spectra were recorded in the Advanced Photon Source (APS) of Argonne
National Laboratory (Argonne, IL USA).
The used solubility apparatus was designed, constructed and validated by us.
Determination of the Ca2+ concentration in the supernatant was done using a Thermo’s IRIS
Intrepid II ICP-OES spectrometer and the solid phase was analyzed by powder X-ray
diffraction (XRD) patterns registered on a Philips PW1710 instrument. The morphologies of
the substances obtained were studied using a Hitachi S-4700 scanning electron microscope
(SEM) and the relative quantities of the ions in the solid samples were determined with a
Röntec QX2 energy dispersive X-ray fluorescence (EDX) spectrometer coupled to the
microscope.
3
3. New results
3.1. Binary systems containing gluconate (Gluc−)
At pH < 11 the Ca2+ ion interacts with the OH group on C2 or C3 of the Gluc−, and
two isomers of the CaGluc+complex are formed in aqueous solution having five- and sixmembered chelate structures and they are in equilibrium.
Investigation of the H+/Gluc− system showed that NMR spectroscopy was suitable to
derive precise stability constants (log Ka= 3.23 ± 0.01), accordingly the Ca2+/Gluc− system
has been studied analogously. From the ionic strength dependence of its formation constant,
the stability constant at 6 ≤ pH ≤ 11 and at I → 0 M has been derived (log K01,1 = 1.5 ± 0.4).
The identification of the binding sites was experimentally approached via twodimensional 1H−43Ca NMR measurements (Figure 1).
Figure 1: The two dimensional 1H – 43Ca NMR spectrum of the system containing Ca2+ and
Gluc− system at pH ~7
4
Figure 2: The suggested structures for the two bonding isomers of the CaGluc+ complex
forming in aqueous solution
Molecular modelling calculations resulted in multidentate bonding isomers with Ca2+ in
bonding interactions with O(C1), O(C2), O(C3) and O(C6) (five-membered chelate, and a
macrochelate reminiscent to scorpionate type compounds), or with O(C1), O(C3) and O(C5)
(six-membered chelate).
3.2. Binary systems containing other sugar derivatives
Scorpionate type complexes with Ca2+ are formed not only with Gluc−, but also with
other simple sugar type ligands (e.g., Hglu−) in aqueous solutions, creating a novel class
of scorpionate complexes.
In order to study the role of various functional groups in carbohydrate derivatives in
complexing to Ca2+ ion, a range of sugar derivatives structurally related to Gluc– has been
selected for further study. The selection criteria were on one hand altering the oxidation states
of the terminal groups and keeping the chain length of the Gluc−, and on the other hand
keeping the oxidation states of the terminal group but increasing or decreasing the chain
length. Investigations of the systems containing glucose (Glu), sorbitol (Sor), mucinate
(Muc2−), heptagluconate (Hglu−) or arabinate (Ara−) have been performed. The techniques
used were multinuclear NMR spectroscopy, potentiometric titration, XAS measurements and
molecular modelling calculations.
5
Figure 3: The optimum geometry found to CaHglu+ scorpionate type complex
3.3. Solubility of Ca(OH)2 in caustic liquors and the role of the Gluc−
In the absence of Gluc−, the CaOH+(aq) is the only water soluble calcium species
beside the Ca2+(aq) being present in strongly alkaline aqueous solutions.
Due to complex formation between the Ca2+ ion and the Gluc− in caustic solutions, the
Ca2+ concentration in the equilibrium liquid phase was found to increase with increasing
Gluc¯ concentration [in the presence of solid Ca(OH)2].
To determine the conditional stability constant of this high–pH calcium–gluconate
complex or complexes, the solubility of Ca(OH)2 in sodium hydroxide solutions was first
studied, and was found to decrease either by increasing the concentration of NaOH or raising
the temperature. Solubility measurements at constant ionic strength [1M (NaCl)] resulted in
the experimental data of the solubility product of Ca(OH)2 and the stability constant of
CaOH+.
Calculations confirmed that the CaOH+(aq) was the only water soluble calcium species
beside the Ca2+(aq) present, and it seems unlikely, that Ca(OH)2(aq) is formed in reasonable
quantities in these systems.
3.4. Equilibria in solutions approaching real Bayer conditions
The behavior of the Gluc− ion in strongly alkaline solution in the presence of Ca2+ or
Al(OH)4− was determined by various techniques.
6
Beside the CaGluc+ and CaGlucH−10 mononuclear complexes, the Ca2Gluc2H−30 biand the Ca3Gluc2H−40 trinuclear complexes are also present in alkaline aqueous
solutions containing Ca2+ and Gluc−; under these conditions unexpectedly stable
complexes are formed via the deprotonation of the alcoholic OH– on the Gluc–.
The NMR study of the Ca2+/Gluc− system showed that chemical exchange between the
various forms of Gluc− was slow at low temperatures (0 − 15 °C) and became fast on the
NMR time scale above 40−45°C also indicating that the alcoholate groups on both the C2 and
C3 carbons participated in Ca2+ binding (Figure 4).
Figure 4: The 1H NMR spectra of the solution containing 0.200 M Gluc– and 0.080 M Ca2+
in the presence of 1.000 M NaOH at different temperatures
Potentiometric titrations on the Ca2+/Gluc− binary system showed that complexation of
Ca2+ with Gluc− in caustic solutions could be reasonably described with four calciumcontaining complexes. Beside the formation of the CaGluc+ (log K110 = 0.34 ± 0.03) and
CaGlucH−10 (log K11−1 = −10.97 ± 0.01) 1:1 ratio complexes, two further polynuclear
complexes ([Ca2GlucH−3]0 and [Ca3Gluc2H−4]0) must have been assumed. The stability
constants of the [Ca2GlucH−3]0 and [Ca3Gluc2H−4]0 complexes are log β22−3 = −33.25 ± 0.02
(= 8.03 ‒ 3 · 13.76) and log β32−4 = −42.65 ± 0.04 (= 12.39 − 4 · 13.76), respectively. When
only mononuclear complexes are formed (pH < 10), two bonding isomers are most likely to
coexist in solution. However at pH ≥ 12 the predominant complex formed is the
[Ca2GlucH−3]0. At reasonably high concentrations of both the metal ion and the ligand, the
trinuclear [Ca3Gluc2H−4]0 complex was formed as follows:
7
CaGlucH−10 + [Ca2GlucH−3]0
[Ca3Gluc2H−4]0
The geometry of the [Ca3Gluc2H−4]0 polynuclear complex was optimized by molecular
modelling calculations. The resulted structure is presented in Figure 5. The central Ca2+
entered into bonding interactions with O(C1) and O(C2) of both Gluc– molecules and the
remaining two Ca2+ atoms form six−membered chelate with the Gluc–, respectively, entering
into bonding interactions with O(C3) and with the other carboxylic oxygen (O’(C1)).
Figure 5: The optimum geometry found for the [Ca3Gluc2H−4] 0 trinuclear complex with two
rendering types (ball-and-stick and spacefilling models)
Binding of the aluminate to gluconate in strongly alkaline solutions (pH > 12) is a pHindependent process (i.e. condensation reaction occurs).
The Al(OH)4−/Gluc− binary system was also investigated. The 1H and
27
Al NMR
measurements confirm the complexation between the Al(OH)4− and Gluc− unambiguously.
The pH potentiometric titration curves were practically identical to those performed in
solutions containing Gluc− only. This fact suggests that binding of Al(OH)4− to Gluc− in these
strongly alkaline solutions (pH > 12) is a pH-independent process. In other words, the
(simplified) condensation reaction
R−OH + Al(OH)4−
R−O−Al(OH)3− + H2O
is likely to take place, which does not involve release or uptake of proton. The stability
constant of the complex was calculated from NMR spectroscopic measurements as new peaks
8
emerge in the 1H NMR spectra of the Gluc− with increasing Al(OH)4− concentration and was
found to be log K1,1 = 2.3 ± 0.4.
In
the ternary
systems
containing
Ca2+,
Al(III) and
Gluc−,
beside the
calcium−gluconate and Al(III)−gluconate binary complexes the [CaAl(OH)4Gluc]0,
[Ca3Al(OH)6Gluc2]+ and [Ca3Al(OH)3Gluc3]3+ are present in solution.
To describe the potentiometric titration curves recorded on the Ca2+/Al(OH)4−/Gluc−
ternary system, the stability constants calculated previously in the Ca2+/Gluc− binary systems
(OH−, GlucH−12−, CaOH+, GlucH−12−, CaGlucH−10, [Ca2Gluc2H−3]0 and [Ca3Gluc2H−4]0) were
held constant.
0.70
[Ca2+]T = 0.0944 M; [Al3+]T = 0.0514 M; [Gluc–]T = 0.1250 M
0.60
[Ca3Al(OH)3Gluc3]3+
Gluc–
[Ca3Al(OH)6Gluc2]+
Fraction of Gluc–
0.50
0.40
CaGluc+
0.30
[Al(OH)Gluc]+
[Al(OH)3Gluc]–
0.20
[CaAl(OH)4Gluc]0
GlucH–12–
0.10
[Al(OH)2Gluc]0
[Ca2Gluc2H–3]0
0.00
2.0
4.0
6.0
8.0
pH
10.0
12.0
14.0
Figure 6: Distribution diagram of the Gluc− containing complex species in the
Ca2+/Al(OH)4−/Gluc− ternary system as a function of pH at I = 1 M (NaCl) and 25.0 °C
The stability constant of the CaGluc+ was found to be log K1010 = 1.08 ± 0.14, and the
species containing Al(III) only were the Al(OH)2+ (log K010−2 = 12.89 ± 0.11), and the Al3+
(log K0100 = 20.94 ± 0.08)
in
the
solutions.
Beside
the
[Al(OH)3Gluc]−
(log β011−1 = 9.89 ± 0.04), [Al(OH)2Gluc]0 (log β011‒2 = 15.01 ± 0.07) and [Al(OH)Gluc]+
(log β011−1 = 19.54 ± 0.06) binary complexes, the formation of the [CaAl(OH)4Gluc]0
9
[Ca3Al(OH)6Gluc2]+
(log β111‒4 = 3.76 ± 0.08),
(log β312−6 = −11.22 ± 0.20)
and
[Ca3Al(OH)3Gluc3]3+ (log β313−3 = 18.59 ± 0.18) ternary complexes were verified.
The distribution diagram of the calcium containing species extrapolated to the
concentration range relevant to the Bayer process ([OH−]T = 2.5 M, [Al(OH)4−]T = 2.0 M,
[Ca2+]T = 0.34 mM and [Gluc−]T = 1 g/dm3), is presented in Figure 7.
1.00
[Ca2+]T = 0.34 mM; [Al3+]T = 2.0 M; [OH–]T = 2.5 M
CaOH+
0.80
[CaAl(OH)4Gluc]0
Fraction of Ca2+
0.60
0.40
[Ca3Al(OH)6Gluc2]+
0.20
[Ca2GlucH–3]–
CaGlucH–10
0.00
0.5
1.0
1.5
2.0
2.5
3.0
3.5
pGluc
4.0
4.5
5.0
5.5
6.0
Figure 7: Distribution diagram of the Ca2+ containing complex species
in the Ca2+/Al(OH)4−/Gluc− ternary system as a function of pGluc.
The grey band refers to the [Gluc−] T = 1 g/dm3.
10
4. Publications
4.1. Journal papers related to the Theses
1.
Multinuclear NMR and molecular modelling investigations on the structure and
equilibria of complexes forming in aqueous solutions of calcium and gluconate
A. PALLAGI, P. SEBŐK, P. FORGÓ, T. JAKUSH, I. PÁLINKÓ, P. SIPOS
Carbohydrate Research 2010. 345 (13). 1856-1864.
IF2010: 1.898
2.
IH: 0
Structure and equilibria of Ca2+-complexes of glucose and sorbitol from
multinuclear (1H,
13
C and
43
Ca) NMR measurements supplemented with
molecular modelling calculations
A. PALLAGI, CS. DUDÁS, Z. CSENDES, P. FORGÓ, I. PÁLINKÓ, P. SIPOS
Journal of Molecular Structure 2011. 993 (1–3). 336-340.
IF2010: 1.599
3.
IH: 0
The solubility of Ca(OH)2 in extremely concentrated NaOH solutions at 25.00 °C
A. PALLAGI, Á. TASI, A. GÁCSI, M. CSÁTI, I. PÁLINKÓ, G. PEINTLER, P. SIPOS
Central European Journal of Chemistry 2012. 10(2). 332-3370.
IF2010: 0.991
IH: 0
4.2. Full papers in conference proceedings related to the Theses
1.
A glükonát/Ca2+ rendszer egyensúlyi kémiája vizes oldatokban (The equilibrium
chemistry of the gluconate/Ca2+ system in aqueous solution)
A. PALLAGI, P. SEBŐK, I. PÁLINKÓ, P. SIPOS
XXXII.
Kémiai
Előadói
Napok
(Chemistry
Lectures),
Program
és
előadásösszefoglalók, ISBN 978-96-3482-969-0, 2009, pp. 169-173.
2.
Structural features of some Ca(II)−sugar complexes forming in aqueous solutions
studied by NMR spectroscopy and computations
A. PALLAGI, Z. CSENDES, P. FORGÓ, P. SIPOS, I. PÁLINKÓ
New Trends in Coordination, Bioinorganic and Applied Inorganic Chemistry,
(Melník, M., Segľa, P., Tatarko, M.), ISBN 978-80-227-3509-4, Press of Slovak
University of Technology, Bratislava, 2011, pp. 442-451.
11
4.3. Conference abstracts related to the Theses
1.
Structural and equilibrium studies on complexes of Ca2+ and gluconate ions in the
aqueous phase
A. PALLAGI, P. SEBŐK, P. FORGÓ, T. JAKUSCH, I. PÁLINKÓ, P. SIPOS
39th International Conference on Coordination Chemistry, Adelaide, South
Australia, 25 − 31 July 2010. (oral presentation)
2.
Structural features of Ca2+-carbohydrate solution complexes studied by
multinuclear (1H, 13C, 43Ca) NMR spectroscopy
A. PALLAGI, P. SEBŐK, I. PÁLINKÓ, P. SIPOS
39TH International Conference on Coordination Chemistry, Adelaide, South
Australia, 25 – 31 July 2010. (poster)
3.
Structure-reactivity relationship of Ca2+–carbohydrate solution complexes studied
by 1H, 13C and 43Ca NMR spectroscopy
A.
PALLAGI,
Z.
CSENDES,
C S.
DUDÁS,
I.
PÁLINKÓ,
P.
SIPOS
EUCMOS, Florence, Italy, 29 August – 03 September 2010. (poster)
4.
A Ca2+ cukorszármazékokkal képzett komplexeinek stabilitása és szerkezete vizes
oldatokban
A. PALLAGI, Z. CSENDES, P. FORGÓ, P. SIPOS, I. PÁLINKÓ
MKE 1. Nemzeti Konferencia, Sopron, Hungary, 22 – 25 May 2011. (oral
presentation)
5.
Structural features of some Ca(II)–sugar complexes forming in aqueous solutions
studied by NMR spectroscopy and computations
A. PALLAGI, Z. CSENDES, P. FORGÓ, P. SIPOS, I. PÁLINKÓ
XXIII. International Conference on Coordination and Bioinorganic Chemistry,
Smolenice, Slovakia, 05 – 10 June 2011. (oral presentation)
12
4.4. Other Journal papers outside the topic of the Theses
1.
The effect of particle shape on the activity of nanocrystalline TiO2 photocatalysts
in phenol decomposition
N. BALÁZS, K. MOGYORÓSI, D. F. SRANKÓ, A. PALLAGI, T. ALAPI, A. OSZKÓ, A.
DOMBI, P. SIPOS
Applied Catalysis B: Environmental 2008. 84 (3–4). 356-362.
IF2008: 4.853
2.
IH: 28
Synthesis and Structural Features of a Novel Ba(II)-Fe(III)-Layered Double
Hydroxide
D. SRANKÓ, A. PALLAGI, I. PÁLINKÓ, E. KUZMANN, S. CANTON, P. SIPOS
Insights into Coordination, Bioinorganic and Applied Inorganic Chemistry 2009.
(Melník, M., Segľa, P., Tatarko, M.), ISBN 978-80-227-3085-3, Press of Slovak
University of Technology, Bratislava, 380-385.
3.
Synthesis and properties of novel Ba(II)Fe(III) layered double hydroxides
D. F. SRANKÓ, A. PALLAGI, E. KUZMANN, S. E. CANTON, M. WALCZAK, A. SÁPI,
Á. KUKOVECZ, Z. KÓNYA, P. SIPOS, I. PÁLINKÓ
Applied Clay Science 2010. 48 (1-2). 214-217.
IF2010: 2.303
4.
IH: 2
Comparison of the liquid and gas phase photocatalytic activity of flamesynthesized TiO2 catalysts: the role of surface quality
N. BALÁZS, A. GÁCSI, A. PALLAGI, K. MOGYORÓSI, T. ALAPI, P. SIPOS, A. DOMBI
Reaction Kinetics Mechanisms and Catalysis 2011. 102 (2). 283–294.
5.
„Safety first!” Munkavédelem és vörösiszap-kezelés Ausztrália egyik legnagyobb
timföldgyárában
A. PALLAGI
Magyar Kémikusok Lapja 2011. 6. 186-187.
full papers, total:
8
related to the topic of the theses:
3
cumulative impact factor, total:
11.644
related to the topic of the theses:
4.448
independent citations, total:
30
related to the topic of the theses:
0
13